1. Field of the Invention
The present invention relates to an information recording method, recording apparatus, reproducing method and reproducing apparatus which scans with heating means recording tracks configured by perpendicular magnetic anisotropy substance and stores information signals by applying a magnetic field to a heated region of the recording tracks.
2. Related Background Art
Various method for reproducing information signals recorded in magnetic recording media are conventionally known. In particular, the present applicant discloses a domain wall displacement type reproducing method in Japanese Patent Application Laid-Open No. 6-290496. This method is characterized by recording on tracks of a magneto-optical medium information signals that are formed by a magnetic domain wall, applying a driving power to this magnetic domain wall so as to rapidly move (displace) the magnetic domain wall, and detecting that movement so as to reproduce the information signals. This method enables recording/reproducing of the information signals with extremely high storing density and high resolution capability.
A method of recording information signals into a magneto-optical medium and a reproducing method for reproducing the information signals by a magnetic wall displacement method will be described below as follows.
FIGS. 10A and 10B are partially enlarged views showing a configuration of a magneto-optical medium 1, where FIG. 10A is a longitudinal section view and FIG. 10B is a plan view. Here, the magneto-optical medium 1 includes a substrate 2 which is configured by a transparent resin material, such as polycarbonate, etc., and is shaped as a belt so that a groove G and a land L are alternately formed in parallel, a magnetic layer 3 formed on the substrate 2 and configured by a perpendicular magnetic anisotropy substance, and a protection coat 4 configured by ultraviolet hardened resin. The magnetic layer 3 formed on the land L forms a belt-shape recording track RT on which information signals are recorded. The magnetic layer 3 is configured by laminating three layers made of a perpendicular magnetic anisotropy substance, a rare earth material such as, for example, Tb, Gd and Dy, and a transition metal such as Fe and Co, etc.; that is, a displacement layer 3a, a switching layer 3b, and a memory layer 3c. Here, the displacement layer 3a is a perpendicular magnetic anisotropy film having magnetic domain wall coercively which is smaller than memory layer 3c and a large magnetic wall movement, the switching layer 3b is a perpendicular magnetic anisotropy substance film having a curie temperature lower than the domain wall displacement layer 3a and the memory layer 3c, and the memory layer 3c is a perpendicular magnetic anisotropy film.
In addition, with a method such as radiating highly powered laser beams locally for heating, etc., a magnetic feature of the magnetic layer 3 on a bottom surface and a side surface of a groove G has been reduced (for example, deterioration of the perpendicular magnetic anisotropy). This weakens magnetic coupling between the recording track RT and a region in which the magnetic feature on its side surfaces has been reduced.
Next, a method to implement thermal magnetic recording information signals to the above-described magnetic recording media 1 with a storing apparatus will be described. The recording apparatus comprises driving means for an optical head, a magnetic head and magneto-optical medium 1. FIGS. 8A and 8B are partially enlarged views of the magneto-optical medium 1, showing a recording method of information signals, where FIG. 8A is a cross-sectional view, and FIG. 8B is a plan view as viewed from the direction of a lower surface. At the time when information signals are recorded, the optical head implements radiation by concentrating a highly powered recording light beam 7 which constitutes heating means for heating a recording track RT through a substrate 2. At the same time, the driving means drives the magneto-optical medium 1, whereby the recording light beam 7 scans the recording track RT in the direction indicated by an arrow A. A temperature of a magnetic layer 3 increases with radiation of the recording light beam 7, and in the periphery of the radiation region of the recording light beam 7 a thermal distribution, shown by isothermal lines in FIG. 8B is formed. Here, a reference numeral 8 denotes an isothermal line of a temperature Tc approximately equal to the curie temperature of the magnetic storing layer 3c. 
Radiation of the light beam 7 by way of an optical head occurs concurrently with the application of a perpendicular magnetic field by the magnetic head, where the direction of the magnetic field is varied upward and downward relative to the radiation region of the recording light beam 7 in accordance with information signals. The memory layer 3c loses magnetization when it passes the front portion of the isothermal line B as a result of its temperature being not less than the curie temperature To, which permits magnetization thereof in the same direction as the magnetic field applied at the time when it passes the back portion of the isothermal line 8 as a result of its temperature being not more than Tv. Moreover, as it moves in a direction more remote from the back portion of the isothermal line 8, the temperature drops while coercively increases, so that the above-described applied magnetization is fixed. Thus, magnetization regions having alternating magnetization in the upward direction and in the downward direction, corresponding with the alternating direction of the applied magnetic livid, are formed in the storing back RT, as shown by arrows in the upward and downward directions in FIG. 8A; in the boundary portion between each magnetization region and the preceding and following magnetization regions, magnetic domain walls W1, W2, W3, W4, W5 and W6 are formed. These magnetic domain walls, which are fanned along the back portion of the isothermal line 5, have an arc shape which bends convexly in the direction opposite from the scanning direction (arrow A) of the light beam 7. In addition, the displacement layer 3a, the switching layer 3b, and the memory layer 3c are mutually brought into exchange coupling so that magnetization and the magnetic domain walls W1, W2, W3, W4, W5 and W6 are transfer-formed onto the displacement layer 3a and the switching layer 3b as well.
The thermal magnetic storing method as described above is referred to as a magnetic field modulation storing method, and can form magnetic walls at an interval shorter than the concentration diameter of the light beam, and therefore is suitable to store information signals at high density.
Next, a method for reproducing information signals from the above-described magneto-optical medium 1 with a reproducing apparatus will be described. The reproducing apparatus comprises driving means for an optical head and magneto-optical medium 1. FIGS. 9A and 9B are partially enlarged views of the magneto-optical medium 1 showing a reproducing method of information signals by way of a displacement layer system, where FIG. 9A is a cross-section view, and FIG. 9B is a plan view as viewed from the direction of a lower surface. At the time when information signals are reproduced, the optical bead implements radiation by concentrating a low power reproducing light beam 9 to a recording back WE through a substrate 2. At the same time, the driving means drives the magneto-optical medium 1, whereby the reproducing light beam 9 scans the recording track RT in the direction indicated by an arrow A. A temperature of a magnetic layer 3 increases with radiation of the light reproducing light beam 9, and in the periphery of the radiation region of the reproducing light beam 9 a thermal distribution, shown by isothermal lines in FIG. 9B, is formed. Here, a reference numeral 30 denotes an isothermal line of a temperature T approximately equal to the curie temperature Ts of the switching layer 3b, and a reference character Xp denotes a position of peak temperature. As described later, in the displacement layer 3a of the recording track RT, the magnetic domain wall is movable only in a region of temperature not less than Ts, that is, a region surrounded by the isothermal line 30; in other regions, movement of a magnetic domain wail is impossible.
Here, in a position sufficiently remote from the radiation region of the reproducing light beam 9, the temperature of the magnetic layer 3 is low and in this position, the displacement layer 3a, the switching layer 3b, and the magneto-optical layer 3c have mutually undergone exchange coupling, and magnetization and magnetic domain wall(s) formed in the magnetic storing layer 3c have been transfer-formed in the switching layer 3b and the displacement layer 3a. In addition, since the temperature distribution is approximately uniform, a driving power sufficient to move the magnetic domain wall transcribed into the displacement layer 3a is not present, and therefore the magnetic domain wall remains fixed. However, as the location draws closer to the radiation region of the reproducing light beam 9, the temperature of the magnetic layer 3 increases, and is subject to passing the forefront portion of the isothermal line 30, where the temperature of the switching layer 3b reaches a temperature not less than Ts, sufficient to cancel magnetization. Thus, since exchange coupling among the displacement layer 3a, the switching layer 3b, and the magnetic memory layer 3c is cut in a region surrounded by the isothermal line 30 higher than Ts, and magnetic coupling between the displacement layer 3a and a region in which both side surfaces of the recording track RT is weakened, the magnetic domain wall will become movable without being restricted. Moreover, since the surrounding temperature is inclined, the driving power will act on the magnetic domain wall in the direction of higher temperature, that is, of lower energy. Thus, the magnetic domain wall (W1 in FIGS. 9A and 9B) which has passed through the forefront portion of the isothermal line 30 moves rapidly toward a position Xp, whose temperature reaches the peak temperature, as shown by arrow B in the displacement layer 3a. Incidentally, in FIG. 9B, the magnetic domain wall W1 prior to movement is indicated by a broken line. Accompanied by movements of this magnetic domain wall, a magnetization region Mex having magnetization in one direction (the downward direction in the example as drawn) is extended and formed. Incidentally, magnetic memory layer 3c is configured by a material having a small degree of displacement of domain wall mobility, and therefore thee magnetic domain wall does not move in the magnetic memory layer 3c.
Thus, the magnetic domain walls W1, W2, . . . W6 successively move toward the position Xp (displace) at respective times when they pass the forefront portion of the isothermal line 30, and each time a respective magnetization region Mex, which alternately has magnetization upward or downward, and is extended in the direction of scanning, is formed. A polarization direction of the reflecting light of the reproducing light beam 9 from this magnetization region Mex is rotated in accordance with the direction of magnetization of the magnetization region Ma due to magneto-optics effect (Kerr effect). Rotation of such polarization is detected using an optical head. The detected signal includes changes in the signal corresponding to movement of the magnetic domain walls, where the magnetic domain wall(s) form information signal domain(s) at position(s) corresponding to the information signal to be stored, and whereby the information signal can be reproduced based on the timing of changes in the reproduced signals.
Problems in recording and reproduction of information signals by way of combination of the above-described conventional magnetic field modulation storing system ad magnetic domain wall mobile reproducing system will be described below.
As described with reference to FIGS. 9A and 9B, according to the magnetic domain wall mobile reproducing system, when the magnetic domain wall passes the forefront of the isothermal line 30, it is no longer restrained by exchange coupling, and moreover temperature inclination generates a driving power that acts to start movement. Incidentally, as shown in FIG. 8B, according to the magnetic field modulation recording system, the magnetic domain wall is formed along the back portion of the isothermal line 8, and thus its shape will be a bent arc that is shaped convex in the direction opposite from the scanning direction (arrow A) of the recording light beam 7, That is, since the scanning direction of the recording light beam and the scanning direction of the reproducing light beam are normally the same, the bending direction of the formed magnetic domain wall is opposite from the bending direction of the forefront portion of the isothermal line 30 at the time of reproduction, as shown in FIG. 9B. Accordingly, as understood with reference to FIG. 9B, at the time of information reproduction, the magnetic domain wall passes the forefront portion of the isothermal line 30 gradually (from the central portion of the arc to the respective end portions of the arc). Thus, the entire magnetic domain wall will not become movable at a single time, and the driving power will not act evenly over the entire arc portion, whereby the start time of the magnetic domain wall movement (displacement) is apt to vary. As a result thereof, jitter of detected signals increases, making exact reproduction of information signals impossible.
In addition, in the case where the forming interval between two magnetic domain walls is short, before both ends of the first magnetic domain wail have passed the forefront portion of the isothermal line 30, the central portion of the subsequent magnetic wall moving layer passes the forefront portion of the isothermal line 30. As a result thereof, signal detection by separating signal changes corresponding with movement of continuous magnetic domain walls becomes impossible, and detection resolution capability drops.
Objects of the present invention are to provide an information recording method, as well as an apparatus, for forming a recording magnetic domain baying magnetic domain walls movable evenly and all together, and to provide a method, as well as apparatus, for reproducing the above-described recording magnetic domain.
The above described objects are attained by the following configurations.
According to an aspect of the present invention, there is provided an information recording method for a domain wall mobile type magneto-optical medium, wherein a light beam scans the medium to heat the medium and at the same time a magnetic field modulated in accordance wit information is applied to a heated point, and a recording magnetic domain having an arc-shaped magnetic domain wall bending convex in a forward direction of an operation of the light beam is formed so that the information is recorded.
According to another aspect of the present invention, there is provided an information recording apparatus comprising an optical head that radiates the light beam for executing the information recording method, a magnetic head that generates a magnetic field modulated in accordance with information, and means for causing the optical head, the magnetic head and the medium to relatively move.
According to a still another aspect of the present invention, there is provided a method for reproducing a recording magnetic domain fanned on a medium by the information recording method by scanning a light beam in a direction along a magnetic domain wail which is bent in a convex state.
Accordingly to further aspect of the present invention, there is provided an information reproducing apparatus comprising an optical head that radiate a light beam and means for causing the optical head and a medium to relatively move in order to execute the reproducing method.
Similar reference characters are used in the FIGURES to denote similar parts for the sake of clarity.